a red rag to a bull

Từ điển Oxford Advanced Learner 8th

a red rag to a ˈbull idiom
(BrE) (NAmE like waving a red flag in front of a ˈbull)something that is likely to make sb very angry
•If you criticize him, it's like a red rag to a bull— he gets absolutely furious.
Main entry: ↑red_idiom